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The most common symptoms of vitamin D deficiency include fatigue, muscle weakness, bone pain, low mood, and frequent illness. In the UK, low sunlight exposure – particularly during autumn and winter, makes deficiency relatively common.
Vitamin D is a fat-soluble vitamin that plays a key role in keeping your bones, muscles, and immune system healthy. When vitamin D levels fall below optimal levels, a deficiency can develop, causing symptoms such as fatigue, muscle weakness and bone pain.
These are some of the most common low vitamin D symptoms, although they can vary from person to person.
While some vitamin D can be obtained through the diet, the majority is produced in your skin when it is exposed to sunlight.
In the UK, limited sunlight – especially during the winter months – means vitamin D deficiency is relatively common, affecting around 1 in 6 adults. For this reason, the NHS recommends taking a daily vitamin D supplement to help prevent deficiency.
This article explores what vitamin D deficiency is, the symptoms you may experience, and who is most at risk.
What is Vitamin D Deficiency?
Vitamin D deficiency occurs when your body does not have enough vitamin D to keep your bones, muscles, and immune system functioning at their best.
This can be confirmed with a simple vitamin D deficiency blood test measuring 25-hydroxyvitamin D (25[OH]D); levels below 25 nmol/L are usually classified as a deficiency.
Although many people do not experience symptoms, those who do may find they get ill more often, experience muscle weakness, or have aching bones. In more severe cases, bone conditions such as rickets in children and osteomalacia in adults can develop.
Below are some of the symptoms you may experience if you have a deficiency:
- Fatigue
- Tiredness
- Bone and joint pain
- Muscle pain
- Muscle weakness
- Low mood or Depression
- Hair loss
- Weakened immune system
Fatigue and Low Energy
Studies have shown that vitamin D deficiency is linked to low energy levels and fatigue. If you feel sluggish despite having adequate sleep, it may be worth getting your vitamin D levels checked.
If you would like to learn more information about whether having a vitamin D deficiency can cause tiredness, and what to do if you are experiencing these symptoms, take a look at our dedicated guide on this.
Bone Pain and Muscle Weakness
Vitamin D helps your body absorb calcium and phosphorus from the food you eat, which are essential for strong and healthy bones. It also plays a key role in muscle function.
Without adequate levels, you may experience:
- Bone and joint pain
- Muscle weakness or spasms
- Increased risk of fractures
Mood Changes and Depression
Low mood or depression can be an unexpected symptom of low levels. Some studies suggest there is a link between vitamin D deficiency and low mood or depression.
However, research findings are mixed, and more studies are needed to fully understand this relationship.
Many factors can affect mood, but if you are experiencing the following symptoms, it may be worth checking your vitamin D levels:
- Lack of motivation
- Low mood
- Poor concentration (“brain fog”)
Hair Loss
Hair loss may be considered a less obvious symptom of vitamin D deficiency. Vitamin D plays an important role in healthy hair growth by helping regulate the hair growth cycle through its different phases. A deficiency may disrupt this cycle, leading to thinning and hair loss.
There are many other causes of hair loss, so it is important to speak to your doctor if you are concerned.
Weakened Immune System
Vitamin D supports the normal functioning of the immune system, including both innate and adaptive responses to infection. Low Vitamin D levels have been associated with an increased susceptibility to infections, particularly respiratory infections such as the common cold and flu.
Research published in the The BMJ found that regular vitamin D supplementation (daily or weekly) may help protect against acute respiratory tract infections.
Less Common or Weird Symptoms Of Vitamin D Deficiency
In addition to common symptoms such as fatigue and muscle weakness, not everyone is the same. Some individuals may experience less obvious or "weird" symptoms of Vitamin D deficiency.
These can include:
- Hair loss
- Low mood or depression
- Brain fog (difficulty concentrating)
- Frequent illness
- Dental and gum problems
Vitamin D Levels and What They Mean
The table below helps to visualise the treatment pathway commonly used by clinicians in the NHS when managing vitamin D levels:
| Vitamin D Level (nmol/L) | Status | Typical Approach |
| <25 | Deficient | Requires a loading dose followed by a maintenance dose |
| 25–50 | Insufficient | Recommended to take a maintenance dose (e.g. vitamin D3 1000 IU once a day) |
| >50 | Sufficient | Levels are sufficient, can take low dose vitamin D supplement to keep levels topped up |
What Causes Vitamin D Deficiency?
Vitamin D deficiency is rarely caused by a single factor. It is more often the result of a combination of influences, including limited sun exposure, diet, lifestyle, medications, and underlying medical conditions.
Sun Exposure
The main source of vitamin D is sunlight. It is produced in the skin when UVB rays convert cholesterol into vitamin D3. Getting enough sun exposure year-round can be difficult in the UK, making this one of the most common causes of deficiency.
Modern lifestyles can also contribute, as people spend more time indoors, including working from home, reducing exposure to natural sunlight.
Diet
Diet plays a secondary role in vitamin D levels, with only around 10% coming from food sources. While diet alone is unlikely to meet daily requirements, consuming vitamin D-rich foods can help support your levels.
Foods that naturally contain vitamin D include oily fish and egg yolks, while others such as milk and breakfast cereals are often fortified.
Vegans and vegetarians may find it more difficult to get enough vitamin D, as most natural sources are animal-based. Although UV-exposed mushrooms and fortified foods can help, their vitamin D content is typically lower. Vegan vitamin D supplements can provide a convenient alternative.
Obesity
Higher levels of body fat are associated with lower vitamin D levels. As a fat-soluble vitamin, vitamin D can become stored in body fat, making it less available in the bloodstream.
Individuals with a BMI over 30 kg/m² may require higher vitamin D intake to reach optimal levels.
Medication
Certain medications can affect how vitamin D is absorbed and processed in the body. Some reduce fat absorption, which in turn reduces vitamin D absorption, while others increase the breakdown of vitamin D, potentially lowering levels over time.
Medical Conditions
Conditions such as Crohn’s disease, coeliac disease, and cystic fibrosis can interfere with the body’s ability to absorb vitamin D from food and supplements.
Kidney and liver conditions can also impact vitamin D levels. The liver converts vitamin D into calcidiol, and the kidneys then convert it into calcitriol – the active form used by the body. Impaired function of these organs can reduce this conversion process.
Who Is Most at Risk of Vitamin D Deficiency?
The NHS recognises several groups of people, who have a higher risk of developing vitamin D deficiency, including:
- People who spend little time outdoors or cover their skin: Limited exposure to sunlight – whether due to lifestyle or cultural/religious clothing can reduce the body’s ability to produce vitamin D naturally.
- Individuals with darker skin tones: Higher levels of melanin reduce the skin’s ability to produce vitamin D from sunlight, increasing the risk of deficiency.
- Pregnant or breastfeeding women: Increased vitamin D requirements to support both mother and baby can lead to lower levels.
- People who are housebound: Limited sun exposure can significantly reduce natural vitamin D production.
- Those taking certain medications: Medications such as anticonvulsants (e.g. carbamazepine, phenytoin), barbiturates, orlistat, and corticosteroids can affect vitamin D levels by altering absorption or metabolism.
- Individuals with certain medical conditions: Conditions such as Crohn’s disease, coeliac disease, ulcerative colitis, cystic fibrosis, and liver or kidney disease can interfere with the absorption or processing of vitamin D.
- Vegans and those following plant-based diets: As most natural sources of vitamin D are animal-based, plant-based diets may increase the risk of deficiency. Vitamin D supplements can help support intake where needed.
How to Improve Vitamin D Levels
Low vitamin D levels are treatable, and there are several practical ways to improve your levels:
Increase Sunlight Exposure
Most vitamin D is produced in the skin through sunlight exposure. Around 20–30 minutes of sunlight per day may be sufficient for many people, depending on skin type and location.
Diet
Including vitamin D-rich foods such as oily fish and egg yolks can help support your intake.
Fortified Foods
Foods such as cow’s milk and plant-based alternatives (e.g. soya milk) are often fortified with vitamin D.
Supplements
Vitamin D3 supplements are a widely used and effective way to prevent and treat deficiency. In the UK, daily supplementation is commonly recommended, particularly during autumn and winter months. Vegan-friendly options are also available.
For those choosing supplements, it is important to look for high-quality products with sensible dosage instructions. One option is Hello Vitamins, which offers a range of vitamin D products formulated by expert pharmacists and designed with quality in mind.
Best Sources of Vitamin D
Natural sunlight remains the best source of vitamin D, although achieving adequate levels in the UK can be challenging, especially during winter.
Dietary sources such as salmon, mackerel, egg yolks, and UV-exposed mushrooms can help increase intake, but this may not always be sufficient. As a result, many people choose to use vitamin D3 supplements for a consistent and convenient intake.
Conclusion
Vitamin D deficiency is a common condition, particularly in the UK. The signs of Vitamin D Deficiency can vary from muscle weakness and fatigue to less obvious symptoms such as low mood or hair loss. In some cases, individuals may have no symptoms at all.
If you are experiencing any of the symptoms mentioned, it may be worth speaking to a healthcare professional for further assessment. With the right management, vitamin D deficiency can be easily treated.
Vitamin Deficiency FAQs
Below are our answers to the most commonly asked questions regarding vitamin D deficiency.
What are the Most Common Symptoms of Vitamin D Deficiency?
The most common symptoms include fatigue, muscle weakness, and aching joints. However, not everyone experiences symptoms, and deficiency can often go unnoticed.
Can Vitamin D Deficiency make you Tired?
Yes, vitamin D deficiency can lead to feelings of tiredness and low energy. This is because vitamin D plays a role in muscle function and energy production. When levels are low, these processes may not work as efficiently, contributing to fatigue.
We have a dedicated article covering this exact question in more detail here.
How Long does it Take to Recover from Vitamin D Deficiency?
Recovery time can vary depending on the severity of the deficiency. With appropriate supplementation, vitamin D levels can gradually improve over a period of weeks to several months.
How Would I Know I am Vitamin D Deficient?
You may experience low Vitamin D symptoms we have mentioned but some people don't have any symptoms at all! Therefore, we would recommend approaching your Doctor for a simple blood test which can be used to diagnose this.
When Is the Best Time to Take Vitamin D?
As vitamin D is a fat-soluble vitamin, it is best taken with a meal to help improve absorption. The most important factor, however, is consistency. Taking it regularly each day will help maintain optimal levels.
Does Low Vitamin D Cause Weight Gain?
There is no direct evidence to suggest that low vitamin D causes weight gain. However, low vitamin D levels have been linked to obesity. This may be because vitamin D is stored in body fat, meaning less of it is available for the body to use.